This invention relates to a method for producing a semi-processed electro-magnetic steel sheet or strip excellent in magnetic properties in the circumferential direction and advantageously employed as the core material for a small-sized electric motor, and a semi-processed electro-magnetic steel sheet excellent in anti-sticking properties and in magnetic properties along the rolling direction.
The semi-processed electro-magnetic steel sheets are mainly employed as the core material for small-sized transformers, electric motors and stabilizers for fluorescent lamps. Recently, in view of the general tendency towards energy saving, an increasing demand is presented for low iron losses and high magnetic permeability.
In small-sized stabilizers and small-sized transformers, in which the direction of the magnetic flux is mainly along the rolling direction of the material, it is preferred that the material exhibits strong anisotropy and good magnetic properties in the rolling direction.
In rotational machines, such as the electric motors, it is preferred that the material has a low anisotropy as the magnetic properties and excellent magnetic properties in the circumferential direction.
As such core material for rotational machines, the Japanese Patent Publication KOKOKU No. 51-942 discloses an in-plane non-oriented magnetic steel sheet having an aggregate texture of [100]&lt;OVW&gt;.
However, in the preparation of the above steel sheet, it is necessary that the hot-rolled sheet be 2.0 to 5.0 mm thick and the reduction ratio for cold rolling be as large as 85 percent or higher, so that the cold rolling performance is exceedingly lowered. Also, because of these constraints of the rolled sheet thickness and the reduction ratio, the product thickness was necessarily limited to not more than 0.35 mm, which represents a drawback of the prior-art steel sheet.
It is an object of the present invention to overcome the above problem and to provide a method for advantageously producing a semi-processed electro-magnetic sheet excellent in the magnetic properties along the circumferential direction without constraints of the reduction ratio and the thickness of the hot-rolled sheet.
Heretofore, an equal number of the 28 cm.times.3 cm epstein samples was usually taken along the rolling direction and in the direction orthogonal to the rolling direction for measuring and evaluating the properties of the electromagnetic steel sheet. This method however has a drawback that, while the magnetic properties can be evaluated in the rolling direction and in the direction orthogonal to the rolling direction, information concerning the magnetic properties in the circumferential direction, required of the dynamoelectric machines, such as the electric moters, cannot be obtained accurately.
In view of the above drawback of the prior art, the present invention is also aimed to provide a method for producing magnetic steel sheet having improved cold rolling properties and various sheet thicknesses. Also, as the method for more reasonable evaluation of the core material for rotational machines, such as the electric motors, there is adopted a method for evaluating the magnetic properties along the circumferential direction using ring-shaped test pieces.
On the other hand, strong anisotropy in the magnetic properties and excellent magnetic properties in the rolling direction are required of small-sized stabilizers in which the magnetic fluxes mainly flow in the rolling direction of the sheet material.
For example, it is reported in the Japanese Patent Application KOKAI No. 53-109815 that a magnetic steel sheet having the magnetic permeability in the rolling direction .mu.15/50 of not lower than 4500 may be obtained for the r.m.s. value of the surface roughness after the skin pass rolling of not larger than 15 microinches.
However, because of the lower surface roughness of the steel sheet obtained by the above prior art method, there is presented a problem that the stacked steel sheets become fused or stuck to one another at the time of stress relief annealing at the user's plant.
For simply avoiding such sticking, it suffices that the steel sheet surface be rough such that the r.m.s. value of the surface roughness be not less than 40 microinches. However, in this case, the magnetic permeability in the rolling direction is necessarily and unavoidably lowered.
The present invention provides a solution of the above problem advantageously and is also aimed to provide a method for producing a semi-process electromagnetic steel sheet excellent not only in anti-sticking performance but also in the magnetic properties, above all, in the magnetic properties in the rolling direction.